Latorre F, Jantzen J P
Klinik für Anaesthesiologie der Johannes Gutenberg Universität Mainz.
Anaesthesist. 1990 Jul;39(7):382-3.
The tidal volume (TV) delivered by conventional anesthesia ventilators is dependent on fresh gas flow rate (FGF). When FGF is reduced, the TV declines; this must be corrected by increasing the ventilator bellows excursion. In addition, the falling bellows produce a negative pressure during the expiratory phase, which may result in positive negative pressure ventilation (PNPV). We have measured the performance of three ventilators: AV 1 (Dräger), VIVOLEC (Hoyer), and ELSA (Engström) that are equipped with a reservoir bag supplied with fresh gas and from which the bellows is filled. METHOD. Two breathing bags with a corrugated tube of 1 m length were connected to a Y-piece to simulate clinical conditions. Starting from 10 l/min, FGF was decreased by 1 l at a time down to 1.0 l/min. Measurements were made at each level of FGF and also at 0.5, 0.3, and 0.2 l/min using a constant inspiration: expiration ratio of 1:2, displacement of the bellows of 700 ml/breath, and a rate of 10/min. Measurements of peak pressure, positive end-expiratory pressure (PEEP), and delivered TV were made at each FGF setting. RESULTS. The course of TV-dependence on FGF is shown in Fig. 1, that of peak inflation pressure and PEEP in Table 1. Reducing FGF had no effect on TV and inflation pressure with ELSA. VIVOLEC lost 17% of the initial TV when FGF was reduced to 0.2 l/min. By closing the relief valve, the loss of TV could be reduced to 4.5%. AV 1 lost about 10% of the initial TV when FGF was reduced to 0.5 l/min. Peak pressure and PEEP were lower with minimal flow. The reservoir bag collapsed when the plateau pressure exceeded 18-20 mbar. CONCLUSIONS. The TV delivered by the ventilators studied was found to reflect closely what had been preset on the bellows displacement scale, within a range of less than or equal to 17%, irrespective of FGF. Hence, the problem of FGF-dependence of TV is largely negated in anesthesia ventilators equipped with a reservoir bag. With ELSA, there was no loss of TV even under minimal flow conditions. VI-VOLEC (with the relief valve closed) and AV 1 had a loss of less than 10% of the initial TV. Adding a reservoir bag to anesthesia ventilators is an effective method of guaranteeing a TV independent of FGF. The three ventilators tested here proved suitable for minimal-flow anesthesia.
传统麻醉呼吸机输送的潮气量（TV）取决于新鲜气体流速（FGF）。当FGF降低时，TV会下降；这必须通过增加呼吸机风箱行程来校正。此外，下降的风箱在呼气阶段会产生负压，这可能导致正负压力通气（PNPV）。我们测量了三种配备有供应新鲜气体的贮气囊且风箱由此充气的呼吸机的性能：AV 1（德尔格公司）、VIVOLEC（霍耶公司）和ELSA（恩斯特龙公司）。方法：将两个带有1米长波纹管的呼吸囊连接到一个Y形接头以模拟临床情况。从10升/分钟开始，FGF每次降低1升，直至降至1.0升/分钟。在每个FGF水平以及在0.5、0.3和0.2升/分钟时进行测量，吸气与呼气比恒定为1:2，风箱位移为700毫升/次呼吸，频率为10次/分钟。在每个FGF设置下测量峰值压力、呼气末正压（PEEP）和输送的TV。结果：TV对FGF的依赖过程如图1所示，峰值充气压力和PEEP的依赖过程见表1。对于ELSA，降低FGF对TV和充气压力没有影响。当FGF降至0.2升/分钟时，VIVOLEC的初始TV损失了17%。通过关闭安全阀，TV的损失可降至4.5%。当FGF降至0.5升/分钟时，AV 1的初始TV损失约10%。在最小流速时，峰值压力和PEEP较低。当平台压力超过18 - 20毫巴时，贮气囊会塌陷。结论：在所研究的呼吸机中，无论FGF如何，输送的TV在小于或等于17%的范围内都能紧密反映风箱位移刻度上预设的值。因此，在配备贮气囊的麻醉呼吸机中，TV对FGF的依赖问题在很大程度上得到了消除。对于ELSA，即使在最小流速条件下也没有TV损失。VIVOLEC（关闭安全阀）和AV 1的初始TV损失小于10%。在麻醉呼吸机上添加贮气囊是保证TV独立于FGF的有效方法。这里测试的三种呼吸机被证明适用于低流量麻醉。
